2006 AMC 12A Problems/Problem 7
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Problem
Mary is $20%$ (Error compiling LaTeX. Unknown error_msg) older than Sally, and Sally is $40%$ (Error compiling LaTeX. Unknown error_msg) younger than Danielle. The sum of their ages is years. How old will Mary be on her next birthday?
Solution
Let be Mary's age, let be Sally's age, and let be Danielle's age. We have , and . The sum of their ages is . Therefore, , and . Then . Mary will be on her next birthday. The answer is B.